Photoradiation method and arrangement

ABSTRACT

A method and arrangement for activating a photoirradiable chemical such as hematoporphyrin derivative (HPD) particularly in vivo by use of pulsed radiation of the required frequency higher energy input with less damage surrounding tissue can be achieved.

BACKGROUND OF THE INVENTION

This invention relates to an arrangement for effecting photoirradiationand to a method of photoirradiation for the activation of chemicalsubstances.

It is known that selective drugs such as hematoporphyrin derivative(HPD) when administered to the animal body firstly can be selectivelyretained in tumours and cancerous tissue and can by effectivephotoirradiation be made to effect by means which are not yet totallyclear, an affect which has a deleterious effect upon the tumour orcancerous tissues.

It is to be realised that while hematoporphyrin derivative is referredto in this specification it is in fact a mixture of compounds and theuse of this invention may extend to particular photosensitive elementsincluded within the compound referred to as hematoporphyrin derivative.

Similarly it can extend to other chemical compounds having a similardeleterious effect on tumours or cancerous tissue.

This invention accordingly relates firstly to a method effecting a moreeffective activation for this purpose of a drug of this type or theinvention relates to the apparatus incorporating the particular partsand characteristics necessary to make the discovery effective or theinvention relates to the treatment of the human body or the inventionrelates to the treatment of any animal body.

Thus far, there has been experienced difficulties in providingirradiation of a selected location with sufficient intensity to ensuresufficient activation of the chemical to effect a sufficient action tohave the desired effect on the tumour or cancerous tissue without theirradiation itself unduly affecting by heating or otherwise thesurrounding flesh.

In the considerable research that has been thus far conducted, there hasbeen difficulty in achieving a sufficiently high irradiation by using aconventional source of radiation without causing this undue damageelsewhere.

SUMMARY OF THE INVENTION

The invention will be better understood when referred to specificillustrations but in general terms according to this invention there isproposed that instead of activating or irradiating the chemical for thepurpose described from a continuous source, there is proposed that thesource is pulsed so that while individual pulses of the radiation energyhave a high energy state, none the less, the average energy andtherefore the general heating of tissue will be somewhat less than wouldbe necessary for a continuous source providing such high energyexcitation continuously.

The effect is to thereby cause the excitation and hence expectedcytotoxic effect while the chemical, particularly hematoporphyrinderivative (HPD), is being held within the tumour in the body.

Accordingly the invention in one form can be said to reside in a methodof preparation of an active compound in vivo comprising the steps ofadministering a photosensitive chemical and irradiating thephotosensitive chemical in situ with pulsed electromagnetic radiation toprepare the active compound.

In one preferred form of the invention the wave length of theelectromagnetic radiation is in the range of from 626 nanometers to 636nanometers.

In a further preferred form the pulse length of the electromagneticradiation is from twenty nanoseconds to fifty nanoseconds and the pulsefrequency is selected from the range of from one hundred hertz to tenkilohertz.

As indicated above in a preferred form of the invention thephotosensitive chemical may be hematoporphyrin derivative.

In one preferred form of the invention the electromagnetic radiation maybe supplied by a gold vapour laser.

In an alternative form of the invention the active compound is of a typeuseful for the treatment of tumours and cancerous tissue.

In an alternative form the invention is said to reside in activation ofa photosensitive chemical comprising the steps of irradiating thephotosensitive chemical with radiant energy as a pulsed supply, suchthat the energy supplied has a multiple number of short pulses of highenergy, but at the same time, has a much lower average energy rate.

In a preferred form of this aspect of the invention the high energyradiation is in the order of tens of kilowatts and the average energyrate is in the order of several watts.

In a further preferred form of the invention the invention may be saidto reside in a gold vapour laser adapted for the treatment of tumours orcancerous tissue, the laser adapted to emit high intensity light at awave length of 627.8 nanometers at a pulse length of from twenty tofifty nanoseconds and a frequency of from one hundred hertz to tenkilohertz.

A discussion of a specific example of this arrangement may be ofassistance in fully understanding the implications of this invention andits application in respect of apparatus appropriate for thisapplication, the method of treating a photosensitive chemical andfinally the method of treatment of either a human body or of an animalbody or the selective destruction of tumours within the human or animalbody.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is known that irradiation of tumours and particularly malignanttumours within the human body following administration of the specificdrug hematoporphyrin derivative with intensive light and in the wavelength range of 626 to 636 nanometers can reduce and in some casestotally destroy the tumour cells.

This specificity of the irradiation range relates both to thesensitivity of the chemical and to the selective transparency of skinand tissue in the human or animal body.

Instant powers of irradiation up to three hundred milliwatts per squarecentimeter have been found necessary to achieve activation sufficient toeffect an adequate cytotoxic effect.

The discovery by this invention has been that by using a pulsed goldvapour laser that this can provide high energy pulses in the order oftens of kilowatts during short repetitive pulses this being directly ina wave length of 627.8 nanometers which is the transition wave length ofthe neutral gold atom.

With a pulse rate of approximately ten kilohertz and a pulse length offrom twenty to fifty nanoseconds average power of several watts can beobtained at conversion efficiencies on the electrical input energytypically 0.3%.

Accordingly in this particular instance there is the dual advantage thatwhile the overall output has an average energy level similar to othersupplies, none the less, the very high energy pulses will give anaccentuated effect with respect to activation of the photosensitivechemical drug while not having unduly high average powers effectinggeneral deterioration of the surrounding tissues by general heating andother effects.

It is of general value that a gold vapour laser is a device which has acompact structure, is relatively straight forward to operate and cangive a low divergent beam suitable for coupling into an optical fibredelivery system which is considered most important and useful indelivering any beam into a suitable location within a human or animalbody.

While reference has been made to the gold vapour laser it is notintended that the invention should necessarily be limited to this. Inits broadest concept it relates to the concept of pulsing the activatingirradiation and as such can relate to all of the generally radiatingsources.

These can be for instance pulsed dye lasers where these are pumped byway of a flash lamp, for example, xenon or a crystal laser or gasdischarge laser or an excimer laser.

Typical of continuous wave lasers which can also be pulsed are a kryptonion laser, argon ion pumped dye laser or perhaps in the future hollowcathode metal vapour lasers. Even sources such as a conventionalfilament lamp source with appropriate filtering, an arc lamp source withappropriate filtering or even a pulsed xenon flash lamp with appropriatefiltering could be used.

What is claimed is:
 1. A method for treating living tissue, wherein the tissue contains an administered hematoporphyrin derivative for sensitizing the tissue to irradiation treatment, the method comprising the step of irradiating the tissue with pulsed electromagnetic energy from a laser having a wave length in the range of 626 to 636 nanometers, the energy having a power level with a peak value on the order of tens of kilowatts, but an average value only on the order of several watts, the peak value being sufficient to activate the hematoporphyrin derivative, but too small to effect general deterioration of surrounding tissue.
 2. A method according to claim 1, wherein the electromagnetic radiation has a pulse length in the range of 20 to 50 nanoseconds.
 3. A method according to claims 1 or 2, wherein the pulse frequency is in the range of 100 hertz to 10 kilohertz.
 4. A method according to claim 1, comprising the step of emitting the electromagnetic energy from a gold vapor laser.
 5. A method according to claim 1, further comprising the step of coupling the electromagnetic energy emitted from the laser into at least one optical fiber for delivery of the energy to a tissue treatment site. 